The sentencing shake-up also sees the government change guidelines to create a 'two-strike' approach to those convicted of a serious sexual or violent crime.

A second offence will result in a mandatory life sentence, which until now have been reserved for murderers.

Prisoners who committed serious sexual or violent crimes will have to serve at least two-thirds of their sentences before being eligible for parole, rather than half their sentences as is the case at present.

Those who are released will be closely monitored for a longer period - up to eight years for sex offenders and up to five years for violent offenders.

"The new regime will restore clarity, coherence and common sense to sentencing... and give victims a clearer understanding of how long offenders will actually serve in prison," justice secretary Ken Clark said.

On knife crime, he added: "We have already announced that we are bringing in an automatic prison sentence for any adults who use a knife to threaten and endanger.

"Clearly any extension of this sentence to children requires very careful consideration. However, we need to send out a clear message about the seriousness of juvenile knife crime."

Shadow justice secretary Sadiq Khan welcomed the move, saying a "clear message" had to be sent to those under 18 that knife crime "is unacceptable and will be punished".

He was more critical of the other sentencing changes, highlighting the limitations of the parole shift and its ability to protect members of the public from unreformed prisoners.

"Under this government's plans, offenders who are a danger to the public could still be released from prison," Mr Khan warned. "They are taking an unnecessary risk with public safety."